Weekly PREP Answers October 22-29
Prep 2006:3
Answer B:
The increased recognition of the health benefits of breastfeeding for infants has resulted in a marked increase in
the breastfeeding rate in the United States, from 33% in 1974 to more than 60% today. Human milk possesses a
number of components not found in cow milk formula that protect against infection, including maternal antibodies
against specific pathogens (eg, immunoglobulin A) and bactericidal compounds (eg, lactoferrin and lysozyme). In
addition, epidemiologic studies suggest the potential for enhanced maturation of the visual system and improved
cognitive development in breastfed infants. For these reasons, breastfeeding until 1 year of age is recommended
by the American Academy of Pediatrics (AAP).
However, many mothers are not willing or able to initiate or continue breastfeeding until 1 year of age.
Fortunately, many excellent infant formulas are available in the United States and in the developed world. These
include cow milk-based formulas, soy-based formulas, casein hydrolysate formulas, and modified amino acidbased formulas. Currently available commercial formulas, if prepared properly, provide adequate amounts of
calories, fat, protein, carbohydrate, minerals, and vitamins, but their composition differs from human milk.
Human milk has a whey-predominant protein; some cow milk formulas contain casein-predominant protein.
Human milk contains docosahexanoic acid, an omega-3 fatty acid that may play a role in human brain and eye
development, and some formulas do not. Although human milk has a lower concentration of protein compared
with formula, both provide sufficient amino acids for the growing infant. Human milk contains lower
concentrations of iron than most infant formulas, but that iron is more bioavailable. In addition, human milk may
contain lower amounts of vitamin D than infant formula, and cases of rickets and hypocalcemia have been
reported in breastfed infants (especially in African-American infants). For this reason, the AAP Committee on
Nutrition recommends a supplement of 200 IU/d of vitamin D for breastfed infants.
Prep 2006:11
Answer D
Although iron deficiency due to inadequate dietary iron with or without anemia has declined with iron fortification
of food, it remains relatively common in the United States. According to the Third National Health and Nutrition
Examination Survey (1988 to 1994), 13% of l-year-olds, 5% of 2-year-olds, 9% of adolescent females (12 to 15
years), and 11% of women of childbearing age (16 to 49 years) were iron-deficient. Iron deficiency anemia was
present in 3% of toddlers, 2% of young adolescent females, and 3% to 5% of women of childbearing age. In
contrast, the prevalence of iron deficiency or anemia is 1% or less among adolescent males.
Dietary iron deficiency in children between the ages of 1 and 3 years often results from ingestion of cow milk, a
very poor source of iron. During adolescence, the demand for iron increases with physical growth to support an
increase in muscle, skeletal, and red blood cell mass. These factors may lead to iron deficiency, particularly when
dietary intake is inadequate. Iron deficiency also may occur in male and female athletes, particularly those
committed to an endurance exercise program, due to uncompensated losses from gastrointestinal or urinary
tracts or from sweat. Adolescent girls, however, have an increased risk of iron deficiency because of menstrual
blood losses. Vegetarians have lower iron stores, but no increase in iron deficiency anemia compared with the
general population. An association between iron deficiency and overweight adolescents has been described.
The adolescent female described in the vignette has a screening hemoglobin concentration that suggests the
presence of mild iron deficiency anemia. Adolescents and young children who have mild-to-moderate iron
deficiency anemia usually have no symptoms and have normal findings on physical examination. Pallor is the
most common sign of anemia. As the degree of anemia worsens, fatigue, exercise intolerance, tachycardia, poor
growth, and splenomegaly may develop. Iron deficiency anemia also is associated with blue sclerae, koilonychia,
and angular stomatitis. During infancy and early childhood, iron deficiency anemia has been associated with
developmental delays and behavioral disturbances. Other observed consequences are increased susceptibility to
infection, pica, and increased gastrointestinal lead absorption that may result in plumbism. Iron deficiency
anemia is not associated with alopecia and hepatomegaly.
Prep 2006:Q100
Answer D
Very low-birthweight (VLBW) infants often are unable to consume enteral sources of nutrition on the first day
after birth. Even when such consumption is possible, they cannot tolerate sufficient volumes of milk to provide
both the fluid and energy requirements for basal metabolism. When disease or distress is present, the energy
requirement increases for the VLBW newborn, and intravenous fluids are required to meet the infant's needs.
Glucose must be provided as an energy substrate to maintain normal metabolism and avoid hypoglycemia, which
is dangerous to the developing central nervous system. A concentration of dextrose 10% in water is
recommended to meet the VLBW infant's energy requirements (5 to 7 mg/kg per minute of glucose) without
providing excessive water. The use of dextrose 5% in water requires volumes of 150 to 200 mL/kg per day to
meet the glucose needs of the VLBW infant. Such volumes are excessive and dangerous, leading to
cardiopulmonary compromise. Saline-containing fluids, such as 0.45% sodium chloride, 0.9% sodium chloride, or
Ringer lactate solution, are unnecessary in the first 24 to 72 hours after birth for most VLBW newborns because
free water losses exceed solute losses and sodium balance is maintained. This period of volume contraction must
occur before saline is provided intravenously.
Prep 2005:82
Answer: C
The most appropriate time to discuss the storage of poisonous substances is at the 6-month health supervision
visit. Prior to 6 months, an infant usually is not sufficiently mobile to be at risk for poisoning. The physician
should not wait until the 9-month or 12-month visits because by those ages, most infants already are mobile
enough to gain access to poisons that are stored in cabinets at floor level and to open cabinet doors. All
poisonous substances should be kept in their original containers and labeled as poisonous. If they are stored in
familiar containers, such as soda bottles, young children may ingest them.
Parents can help protect their children further from poisoning by purchasing medicines that have childproof caps
and keeping the phone number of their local poison control center easily available. Poison control centers often
are much better resources than a 911 operator or a personal physician for the initial management of a suspected
poisoning. These centers maintain data on the signs and symptoms associated with ingestion of household
products, medications, and plants as well as the appropriate management of ingestions.
Although parents used to be advised to have ipecac in the home for emergency use, the American Academy of
Pediatrics no longer recommends this. Research has shown that even when ipecac is administered immediately
after the ingestion of a substance, it does not remove the substance completely from the stomach. Adverse
effects include persistent vomiting, lethargy, and diarrhea. Another shortcoming of home ipecac therapy is that
continued vomiting may result in the child being unable to tolerate other orally administered poison treatments,
such as activated charcoal.
Prep 2005:186
Answer a
The child described in the vignette has symptoms (eg, tachycardia, lethargy, dilated pupils) suggestive of tricyclic
antidepressant (TCA) ingestion. TCAs have been a commonly prescribed group of drugs, although with the
introduction of the newer class of antidepressants, serotonin reuptake inhibitors, the use of TCAs has declined.
Nonetheless, toxicity from TCAs remains an important cause of morbidity and mortality in children.
When TCAs are ingested in toxic amounts, they affect primarily the central nervous and cardiovascular systems.
Central nervous system signs and symptoms of TCA toxicity include irritability, euphoria, seizures, and
unresponsiveness. There also may be autonomic nervous system symptoms, such as mydriasis, dry skin, dry
mouth, urinary retention, and tachycardia. Among the direct effects on the cardiac system are a delay in signal
conduction through the bundle of His, depression of myocardial contractile function, and prolongation of the QRS
and the QT intervals. These latter cardiac effects may potentiate arrhythmia formation.
Electrocardiography is essential in the evaluation of the child suspected of having a TCA toxic ingestion. The
voltage intervals should be measured, with particular attention to the QRS duration and the QT interval. A QRS
duration of greater than 100 msec is associated with the development of seizures; a QRS duration of more than
160 msec is associated with ventricular dysrhythmias that may be very difficult to treat. These ventricular
dysrhythmias are potentially fatal.
Electroencephalography does not play a role in the initial evaluation and management of children in whom a TCA
toxic ingestion is suspected. Seizures, when they occur, usually do so early in the course and often resolve
without anticonvulsant therapy. The signs and symptoms displayed by the patient in the vignette are not
consistent with digoxin ingestion or toxicity, and, therefore, evaluating serum digoxin levels is not indicated in
this patient. Serum drug levels of TCAs can be measured to confirm the diagnosis, but this is not helpful in the
prognosis or management of TCA ingestion. Serum electrolyte levels may be obtained, but they have no
predictive value in the management of TCA toxicity.